Television synchronizing system



a 1941- R. B. DOME ETAL 2,

TELEVIS ION SYNCHRONI Z INCT SYSTEM Filed 001;. 26, 1958 Inventors:Robert B. Dome,

Robert E. M e, y JV a) T-he 'r Attorneg.

tented Jan. 28, 1941 .1 lTE STATES mater PATEN OFFW TELEVISIONSYNCHRONIZING SYSTEM Application October 26, 1938, Serial No. 237,025

13 Claims.

Our invention relates to an improved synchronizing arrangement for atelevision system and more particularly to a circuit arrangement forseparating in such systems the vertical from the horizontalsynchronizing impulses.

In television systems involving operations of incremental picture areatraversal at the transmitter and receiver, it becomes necessary bywhatever method such operations are performed to insure that theperiodicity of a complete traversal is the same at both the transmitterand the receiver. The prevalent use of the cathode ray type of tube forthe purpose of converting the image to be transmitted into electricalimpulses and for reconverting the electrical impulses into a visibleimage at the receiver has led to the practical transmitting on thecarrier wave the picture or so-called video signal component and, inaddition, a synchronizing component which after separation from thepicture component may be used to synchronize the timed scanning movementof the electron stream in the cathode ray tube of the receiver with thatof the cathode ray tube of the transmitter. Since the horizontal andvertical synchronizing impulses are transmitted on the same carrierwave, it becomes necessary to separate them in the television receiverin order that each may be television system a greatly simplified and improved arrangement for separating the vertical from the horizontalsynchronizing impulses.

A further object of our invention is to provide a separating circuit forthe synchronizing impulses which operates to give a materially improvedaccuracy in the synchronized operation of the vertical oscillatoremployed in the television receiver. I

Another object of our invention is to provide a separating circuit forthe synchronizing impulses which does not require the use of anyequalizing pulses and one which, therefore, does not depend for theaccuracy of its separation upon the transmission of any synchronizingimpulses preceding the vertical synchronizing impulses.

An additional object of our invention is to provide a synchronizingimpulse separating circuit which operates to accomplish in a completeand clean-cut manner the entire separation of the vertical synchronizingimpulses from the horizontal synchronizing impulses.

The novel features which we believe to be characteristic of ourinvention are set forth with particularity in the appended claims. Ourinvention itself, however, both as to its organization and method ofpperation together with further objects and advantages thereof may bestbe understood by reference to the following description taken inconnection with the accompanying drawing in which Figure 1 represents anembodiment of our invention, and Figure 2 illustrates graphically thepotential vrelationships at selected points in a system embodying ourin-- vention.

Referring more particularly to Figure 1 of the .drawing, we haveillustrated our invention as embodied in an arrangement for separatingin a television receiver the synchronizing impulses from the picture orvideo signal and for thereafter, in accordance with our invention,separating the vertical from the horizontal synchronizing impulses. Thetelevision signal, after being received and amplified by circuitelements, not shown, is supplied through the circuit l0. H to a dioderectifier l2 and series connected diode load resistors l3, 14. Theresistor I3 is by-passed by a condenser IS, the time constant of theresistor 13 and condenser l5 being large in comparison with GO-cycleswhich is the rate of occurrence of the vertical synchronizing impulses.The potential drop appearing across the resistors l3 and I4 is suppliedthrough a ripple filter, comprised by a resistor l6 and condenser H, toan automatic volume control conductor 3 which may be connected tocontrol the gain of preceding amplifier stages, not shown, in a mannerwell known in the art.

The potential appearing across the resistor 54 is supplied through acondenser H! to the control grid 20 of the first one of a pair of triodetype electron discharge devices included within the envelope 2|. Thistriode has, in addition to the control grid 20, a cathode element ZZ-andan anode element 23. The cathode is connected directly to ground andthrough a resistor 26 to the grid 20 while the anode is connectedthrough a resistor 24 and a conductor 25 to the positive terminal of asource of anode potential, not shown. A condenser 21 maintains theconductor 25 at ground potential for alternating currents having thefrequency of those which flow through the resistor 24.

The alternating current potentials appearing between ground and theupper terminal of the resistor 24 are supplied through a'condenser 28 tothe control grid 29 of the second triode elec tron discharge deviceincluded within the tube envelope 2|. The circuit connections of thesecond triode are similar to those of the first triode,

the cathode 30 being directly connected to ground, the anode 3| beingconnected through a resistor 32 to the conductor 25, and a resistor 33being used to connect the grid 29 with the oathode 30.

The alternating current potential appearing between ground and the upperterminal of the resistor 32 is now supplied through a condenser 34 to asynchronizing impulse separator arrangement constructed in accordancewith our invention. Thisarrangement includes a first triode type ofelectron discharge device enclosed within the tube envelope 46, whosecontrol grid 35 and cathode 36 are connected to have impressed thereonthe alternating current potential supplied through the condenser 34. Theanode 31 of this triode is connected to groundthrough a pair of paths,the first of which is comprised by a condenser 38 and a resistor 39,while the second is comprised by a resistor 49, a conductor 4|,

and a source of anode potential, not shown. The

triode, as thus connected, operates as will be explained in detailhereinafter to change the synchronizing impulses into abrupt transientpotential impulses across the resistor 39.

These transient potential impulses are supplied through a series circuitcomprised by a parallel connected condenser 42 and resistance 43 andthrough a diode rectifier 44 tothe control grid 45 of a second triodetype of electron discharge device included within the tube envelope 46.The second triode has a cathode ele-- ment 41 connected to ground and ananode element 48 which is connected through a resistor 49 to'theconductor 4| .and therethrough to a source of anode potential, notshown. A resistor 50 is connected between thegrid 45' and the cathode 41of the second triode. The amplified transient potential impulses whichappear between ground and the upper terminal of the resistor 49 aresupplied through a condenser 5| to a resistor 52 and to a circuit 53, 54so connected as to control the timed oscillation of a verticaloscillator, not shown, thereby to control the timed movement of thereceiver cathoderay as it moves from the upper to the lower edge of thereceiver cathode ray tube screen, also not shown.

The synchronizing pulses appearing in the output circuit of the tube 2|are also supplied through the condenser 34 and through a conductor 55 tothe control grid 56 of an electron discharge device 51. The device 51 isconnected as an amplifier with a biasing resistor 58 and parallelconnected condenser 59 included in its cathode circuit and with itsanode 50 connected through a resistor BI and the conductor 4| to asource of anode potential, not shown. A small condenser 62 is connectedto supply only the relatively high frequency horizontal synchronizingpulses which appear in the anode circuit of the discharge device 51 to aresistor 63 and to the control circuit conductors 64, 65. The horizontalpulses arethereafter used to control the timed oscillation of ahorizontal oscillator, not shown, which may be connected in a mannerwell known in the art to control in the cathode ray tube, not shown, themovement of the cathode ray as it moves horizontally across the cathoderay tube screen.

The operation of our invention will now be explained by the aid of thecurves shown in tion the use of any equalizing pulses.

Figure 2 of the drawing. The television carrier wave is received andamplified by apparatus, not shown, after which it is supplied to theinput circuit I0, I] of Fig. 1. The wave at this point is symmetricalabout a reference axis and its general form is as illustrated in Figure2a. where only the lower half of the carrier wave envelope (lying belowthe reference axis 0, O) is shown for purposes of convenience. Thecarrier wave consists, as is well known in the art, of a picture orvideo signal portion 1 which controls the instantaneous intensity of thecathode ray as it sweeps across the cathode ray tube screen to form thetelevision picture. Between the video signals ,f are the so-calledblanking pedestals g which serve to extinguish the cathode ray in orderthat the cathode ray tube screen will not be illuminated during thereturn movement of the cathode ray across the screen at the end of eachhorizontal traversal. The wave shown in Figure 2a is of the negativetransmission type in which the amplitude of the pedestal g from thereference axis 0, 0 corresponds to the black portion of the picturewhereas a point on the television signal j close to the line 0, 0corresponds to white in the picture. Superimposed on the pedestals g arethe horizontal synchronizing impulses h which, being of greateramplitude than the pedestals 9, lie in the relatively black region knownas blacker-than-black. The synchronizing impulses It therefore cannot beseen in the reproduced image, since no point on the image can be blackerthan that corresponding to the amplitude of a pedestal g. These impulsesmay be separated from the composite television picture in a. mannerpresently to be described to control the horizontal oscillator of thereceiver. That portion of the television signal lying to the right ofthe last picture or video signal I and extending to the next videosignal, not shown, (but which would appear off of the right-hand edge ofthe drawing) is the portion of the signal during which the cathode rayis extinguished to allow the ray to return from the lower edge of thepicture to the upper edge of the picture to begina new picture frame.During this interval, the conventional carrier wave includes a number ofso-called equalizing pulses i, of double the frequency and one-half thedurasynchronizing pulses i. The wave shown in Fig.

2a is the wave which has been adopted as standard for the United Statesby the Radio Manufacturers Association and tentatively adopted by theFederal Communications Commission. It will become apparent as thedetailed operation of our invention is described that our invention doesnot require for its proper opera- The time required for the equalizingpulses may with our invention be devoted to more useful purposes.

The composite television signal shown graphiing a magnitude as indicatedby the broken line m, m of Figure 2a, and this potentialbiases the anodeof diode l2 negatively with respect to the cathode by an amountcorresponding to the distance between lines 0 and m of Fig. 2a. The peakof each synchronizing pulse causes the diode anode to become positivewith respect to its cathode and thereby produces a current flow throughthe resistor l4, the current having a wave shape corresponding to thatof the synchronizing pulse. The picture or video signal I having asmaller amplitude, is not effective to produce current in rectifier l2and is thus eflectively separated from the synchronizing impulses h, z,and k.

The potential appearing across the resistor l4, and which has the formindicated by the graph illustrated directly above resistor M in Fig. 1,is supplied through the condenser I9 to a limiter circuit comprised bythe several electron discharge devices included within the envelope 2|and their associated circuit. The limiter circuit operates in a mannerwell known in the art both to amplify the synchronizing impulses,thereby to increase their amplitude, and to shape to a square wave formthe top and bottom of each.

The wave form of the potential appearing acrossthe resistance 32 in theoutput circuit of the limiter is shown in Figure 2b.

The potential appearing between ground and the upper terminal of theresistor 32 is supplied through a condenser 34 to the grid 35 of thefirst triode included in the tube envelope 46. Each synchronizingimpulse p, q, and 1' has a polarity such that it biases the first triodeto cut-01f so that no current flows from the anode 31 to the cathode 36..The condenser 38 thereupon starts charging through the resistors 39 and40. As soon as a respective synchronizing impulse p, q, or r iscompleted, the negative bias is removed from the grid 35, theanode-cathode impedance of this triode abruptly decreases, and thecondenser 38 thereupon discharges through the anode to cathode path andthrough the resistor 39. The vertical synchronizing pulses r are oflonger duration than the horizontal synchronizing pulses p and thereforeprovide a longer time in which the charge may accumulate in thecondenser 38. The potential appearing across the terminals of thecondenser 38 during its charging interval may be represented by thecurve of Figure '20. It will be evident from this curve that the maximumamplitude of the potential s appearing across the condenser 38corresponding to the horizontal synchronizing pulses p is smaller thanthat of the potential t corresponding to the vertical synchronizingpulses 1.

Both the charging and the discharging currents of the condenser 38 flow,as previously stated, through the resistor 39. The potential appearingacross this resistor may be represented by the curve of Fig. 201 wherethe flat topped loops correspond to the charging currents and thevertical lines correspond to the abrupt transient potential impulsesproduced by the discharge currents. The discharge currents correspondingto the potentials s of Figure 2c are 4 smaller than the dischargecurrents corresponding to the relatively larger potentials t andtherefore produce across the resistor 39 transient potentials u smallerin magnitude than the transient potiential pulses 1;. It is important tonote that the transient potential pulses u and 1) occur on the laggingedge of the synchronizing impulses. It has been found that this producesa very materially improved synchronization of the television receiverunder adverse atmospheric receiving conditions.

The potential pulses appearing across the resistor 39 are suppliedthrough the resistance 43 and parallel connected condenser 42 andthrough the diode rectifier 44 to the grid of the sec- 0nd triode deviceincluded within the tube envelope 46. The time constant of the condenser42 andresistor 43 is so chosen that the first few synchronizing pulsesof each transmission charge the condenser 42 to a potentialwhosemagnitude may be represented by the broken line w, w of Figure 2d.The polarity of this charge is such that the anode element of the dioderectifier 44 is biased negatively with respect to the diode cathode. Itwill thus be evident that the potential pulses appearing across theresistor 39 are ineffective to' produce a flow of current through theresistor 43, the diode rectifier 44, and the resistor until thepotential pulses have a magnitude greater than that represented by thebroken line 10, w. Since only the potential pulses 1) which result fromthe vertical synchronizing impulses have the required amplitudenecessary to produce such fiow of current, the potential pulsesappearing across the resistor 59 may be represented graphically by thecurve of Figure 2e'. Each of the potential pulses of Fig. 2e has anamplitude proportional to that value of the potential pulse 1; in excessof the potential represented in Figure 2d by the broken line 10, w.

The potential at any instant on the grid 45 of the second triode isdetermined by the voltage drop across the resistor 50. It will thus beap-' parent that since the horizontal potential synch'ronizing pulsesappearing across the resistor 39 produce no current flow in the resistor50 the} have no control over the potential of the grid 45 and,therefore, are effectively separated from the vertical synchronizingpulses. The potential pulses appearing across the resistor 50 areamplified by' the second triode discharge device included in theenvelope 46 and are thereafter supplied through the control conductors53, 54 to control the timed oscillation of a vertical oscillator, notshown, included in the television receiver.

Both the vertical and horizontal synchronizing impulses appearingbetween ground and the right-hand terminal of the condenser 34 aresupplied to the control grid 56 of the electron discharge device 51. Theamplified impulses are supplied to an output circuit comprised by thecondenser 62 and resistor 63. The condenser 62 has a relatively smallcapacity and therefore presents a relatively high reactance to the lowfrequency vertical synchronizing impulses but a relatively low reactanceto the much higher frequency horizontal synchronizing impulses. Only thehorizontal impulses are therefore supplied with appreciable magnitudethrough the capacitor 62 to the control circuit 64, 65 to control thetimed oscillation of the horizontal oscillator, not shown included inthe television receiver.

It will now be evident that a synchronizing impulse separatorarrangement constructed in accordance with our invention operateswith aminimum of apparatus to accomplish the complete separation of thevertical from the horizontal synchronizing impulses which appear in thesynchronizing circuit of a television receiver. It will further beevident to one skilled in the art that our invention accomplishes in asimplified and improved manner a more perfectly timed contional pulsesto said generator, said means beingtrol of the vertical oscillator ofthe television receiver since the triggering of the oscillator occurs onthe lagging edge of the synchronizing impulse rather than according topresent practice, on the leading edge where the triggering may be soeasily upset by extraneous noise impulses received with the televisionsignal. Our invention has the additional important advantage that itdoes not depend for its operation upon the transmission of anyequalizing pulses and the impairment of the reproduced image, which maybe caused by improper synchronization resulting from-the failure toreceive the proper number of equalizing pulses entirely free of noisedisturbances and of the required amplitude, is thereby avoided. Byomitting the equalizing pulses, a greater portion of the availabletransmitting time may be devoted'to the transmission of the picturesignals thereby to provide a larger picture area.

While we have shown a particular'embodiment of our invention, it will,of course, be understood that we do not wish to be limited thereto sincediflerent modifications may be made both in the circuit elements andtheir arrangements. We, of course, contemplate by the appended claims tocover any such modifications as fall within the true spirit and scope ofour invention.

What we desire to claim by United States Letters Patent is: i

1. In a television system, the combination of a source of synchronizingimpulses to be separated, said impulses being of different duration,means responsive to each of said impulses to produce a correspondingpotential pulse having an intensity dependent upon the duration of therespective synchronizing impulse, and means responsive to termination ofthose of said corresponding potential pulses having an intensity greaterthan the intensity of the weaker of said corresponding potential pulsesto supply addiunresponsive to said weaker of said potential pulses tosupply such additional pulses, whereby the longer of said impulses ofdifferent duration are separated from the shorter thereof.

2. In a television system, the combination ,of a source of synchronizingimpulses to be separated, said impulses being of different duration,means responsive to each of said impulses to produce a correspondingpotential pulse having an intensity dependent upon the duration of therespective synchronizing impulse, an impulse generator to besynchronized, and meansrespom.

sive to termination of each of said impulses for producing a transientvoltage dependent in intensity upon the intensity of the respectivepotential pulse, and amplitude selecting means responsive only to themore intense of said transient voltages to supply voltage impulses tosaid oscillator.

3. In a television system, the combination of a source of synchronizingimpulses to be separated, said impulses having differing duration, a.condenser, means for charging said condenser to an extent dependent uponthe duration of each of said synchronizing impulses and for dischargingsaid condenser at the cessation of each of said impulses, meansresponsive to each discharge current of said condenser for producing apotential pulse whose magnitude varies in proportion to the magnitude ofsaid discharge current, a scanning device, and means for transmitting apulse to said scanning device in response to each of said potentialpulses having said means being unresponsive to said weaker pulses.

4. In a television system in which synchronizing impulses of differentduration are to be separated, the combination of means for convertingsaid impulses of different duration to impulses of different intensity,a unidirectional current conducing path, means to supply a bias voltageto said path polarized to render it noneconductive, means to supply saidimpulses of difierent. intensity to said path polarized in theconducting direction of said device, the stronger of said impulses beingof such magnitude as to overcome said bias and produce a current impulsethrough said path and the weaker of said impulses of different intensitybeing insuflicient to overcome said bias whereby said impulses ofdifferent duration are separated.

5. In a synchronizing system for television, the combination of a sourceof synchronizing impulses of differing duration, an electron dischargedevice having a control element, means for supplying synchronizingimpulses from said source to said control element thereby to control theconductivity of said device, a condenser, means controlled by saiddevice for charging said condenser throughout the duration of each ofsaid synchronizing impulses thereby to produce a charge thereindependent in magnitudeupon the duration of the respective synchronizingimpulses and for abruptly discharging said condenser at the cessation ofeach'of said impulses, means responsive to each discharge current ofsaid condenser for producing a potential pulse whose magnitude independent upon the magnitude of said discharge current, a translatingdevice, and means for transmitting to said translating device theportion of any of said potential pulses in excess of a predeterminedmagnitude.

6. In a television system, the combination of a source of synchronizingimpulses of differing duration, an electron discharge device having acontrol element, means for supplying synchronizing impulsesfrom saidsource to said control element thereby to control the conductivity ofsaid device, a: condenser, means for charging said condenser throughoutthe duration of each ofi said synchronizing impulses and for dischargingrent of said condenser for producing a potential pulse whose magnitudevaries in proportion to the magnitude ofsaid discharge current, aunidirectional current conducting path, means including said path fordistinguishing between potential pulses having an amplitude smaller orgreater than a predetermined amplitude, a translating device, and meansfor supplying to said translating device the portion of any of saidpotential pulses in excess of said predetermined amplitude.

7. In a synchronizing system for a television receiver, the combinationof an electron discharge device having a control electrode, an anode anda cathode, a source of horizontal and vertical synchronizing impulses,said vertical impulses being of longer duration than said horizontalimpulses, means for supplying said impulses to said control electrode ina manner to bias saidelectrode more negatively thereby abruptly toincrease the anode to cathode impedance of said device whereby saidanode to cathode impedance abruptly decreases upon ter- Ill accusesrnination oi any of said impulses, a condenser, a source atunidirectional potential, means responsive to the impedance of saiddevice for charging said condenser irom said last named source to anerrtent dependent upon the duration of said impulse supplied to saidcontrol electrode and abruptly to discharge said condenser upon terrnination of said impulse, a translating device, and means forreflecting control of said translatinp device by discharge currents ofsaid con denser in excess oi a predetermined value.

c, in a synchronizing irnpulse separator for television system, thecombination of a source at horinontal and vertical synchronisingimpulses to he separated, said vertical synchronisrint, inipulsesdiderine in duration from said horizontal svnchronisine impulses, meansresponsive to the cessation of each of said synchronising impulses torproducing a potential pulse, the nuaenitude at said pulses varyingsuhstantially in direct proportion to the duration of each initiatingimpulse, and means responsive to the magnitude of said potential pulsefor distinguishing those po-'- tcntiai pulses which correspond either tosaid horinontal or to said vertical synchronizing lrn-' pulses,

h. in a television receiver in which scanning impulses oi diuerentduration are received and separated and supplied to separate channels,the method which includes storing each of said impulses to produce apotential having a value dependent upou the duration oi? the respectivestored impulse, and transmitting to one or said channels only saidimpulses which produce potentials which exceed a predetermined value increase of the potential produced by storing the shorter of saidimpulses.

it, in a television receiver in which scanning impulses are received andseparated for transmission. to separate channels, a condenser, means tostore each of said impulses in said condenser to produce a chargethereon dependent upon the duration of the respective impulses, means tomined value, and means to transmit to the other channel impulses which,when stored, produce potential of less than said value. p

ii. In a television receiver in which scanning impulses are received andseparated for transmission to separate channels, a condenser, means tostore each of said impulses in said condenser to produce a chargethereon dependent upon the duration of the respective impulses, means todischarge said condenser through an impedance in one of said channelsafter termination oi each impulse, and means connected across saidinnpedance to pass current only in response to po tentials on saidimpedance in excess oi the potential produced hp discharge at saidcondenser alter storing of a shorter oi said impulses.

12. Ina television svstern in which synchronizing impulses of diiler'entduration are to he separated, the combination oi means to convert thetill synchronizing impulses oi different duration to transient pulse atthe end of each of said impulses of difierent amplitude, amplitudeselecting said transient pulses of greater magnitude from said transientpulses of smaller magnitude. and frequency selecting said synchronizingpulses of o lesser duration from those of greater duration.

ROBERT B. DOME.

ROBERT E. MOE.

